[libc] Fix malloc riscv32 test failures from #117815

Author: mysterymath

libc/test/src/__support/block_test.cpp

@@ -75,8 +75,11 @@ TEST(LlvmLibcBlockTest, CannotCreateTooSmallBlock) {
 
 TEST(LlvmLibcBlockTest, CanSplitBlock) {
   constexpr size_t kN = 1024;
-  // Give the split position a large alignment.
-  constexpr size_t kSplitN = 512 + Block::PREV_FIELD_SIZE;
+
+  // Choose a split position such that the next block's usable space is 512
+  // bytes from this one's. This should be sufficient for any machine's
+  // alignment.
+  const size_t kSplitN = Block::inner_size(512);
 
   array<byte, kN> bytes;
   auto result = Block::init(bytes);

libc/test/src/__support/freestore_test.cpp

@@ -26,6 +26,10 @@ TEST(LlvmLibcFreeStore, TooSmall) {
   Block *too_small = *maybeBlock;
   maybeBlock = too_small->split(Block::PREV_FIELD_SIZE);
   ASSERT_TRUE(maybeBlock.has_value());
+  // On platforms with high alignment the smallest legal block may be large
+  // enough for a node.
+  if (too_small->outer_size() > sizeof(Block) + sizeof(FreeList::Node))
+    return;
   Block *remainder = *maybeBlock;
 
   FreeStore store;